Cleanup the WSGI app reference from the threadlocal state on every request.

Change-Id: I22f93224047e2b6fd6692423cc27f85b6261f9f8
Closes-Bug: #1279461

pecan/core.py

@@ -598,3 +598,4 @@ class Pecan(object):
             del state.request
             del state.response
             del state.controller
+            del state.app

pecan/tests/test_base.py

@@ -972,7 +972,7 @@ class TestThreadLocalState(PecanTestCase):
         assert r.status_int == 200
         assert r.body == b_('/')
 
-        assert list(state.__dict__.keys()) == ['app']
+        assert state.__dict__ == {}
 
 
 class TestFileTypeExtensions(PecanTestCase):